The invention relates to a pump, in particular for cooling water of the motor vehicle. In the automotive sector, the waste heat of the internal combustion engine is reduced, for example, by improving the efficiency. The combustion heat is conveyed via both the heat exchanger for the interior as well as via the radiator grill so that when cold starting in winter, the passenger compartment is relatively slow to heat. In order to increase comfort, electrically operated auxiliary water pumps are increasingly used in order to be able to heat the interior in a concerted manner.
A pump of this kind, with an impeller wheel supported in rotary fashion in a pump chamber, an excitation device for driving the impeller wheel to rotate, and a control circuit for the excitation device has been disclosed by DE 44 11 960 A1. In this known pump, the excitation device and the control circuit are accommodated in a common essentially cylindrical chamber, which is hermetically sealed in relation to the pump chamber and protrudes into it.
The impeller wheel is connected to an annular rotor which extends around the excitation device in an annular part of the pump chamber. With this construction, waste heat from the excitation device can flow into the pump fluid only through the wall of the pump chamber and the impeller wheel that overlaps the pump chamber in the axial direction. The flow of heat in the radial direction is only possible through two walls and the rotor. However, the control circuit that is mounted on a printed circuit board is subjected directly to the waste heat. The maximal operating temperature of this pump is consequently determined by the limited temperature resistance of the material of the printed circuit board and/or the softening temperature of the solder used to mount the components of the control circuit on the printed circuit board.
During assembly of the pump, it is necessary to slide the excitation device and the printed circuit board with the control circuit into the corresponding chamber through a rear opening and then to close the opening with a cover, which has a plug formed onto it for the power supply contacts of the control circuit. An electrical contact between the plug and the control circuit is thereby produced with the aid of pins, which are mounted on the printed circuit board and, during attachment of the cover, are slid into a bushing affixed to the cover. The bushings are fitted onto the pins blind; it is therefore difficult to detect and correct bad contacts in which the pin and bushing are not engaged in one another as desired. The quality of an insertion connection of this kind can deteriorate if it is subjected to intense temperature changes or high temperatures.
It is therefore expected that in the near future, there will be a demand in automotive engineering for cooling water pumps which are in a position to withstand permanent operating temperatures of 130 to 140xc2x0 C. this arises not only from the fact that higher cooling water pressures and cooling water boiling temperatures are provided but also from the fact that with continuing miniaturization of the auxiliary units installed in motor vehicles, which also include a cooling water pump, the power density of these units increases and consequently, the operating temperature of the units increases as a result of self heating.
However, printed circuit boards and solders that are suitable for such operating conditions are expensive.
The invention proposes a pump construction with the features mentioned at the beginning in which the control circuit and the excitation device are thermally separated from each other by the pump chamber. With an arrangement of this kind, the waste heat of the excitation device is essentially absorbed and removed by the cooling water flowing through the pump chamber so that this waste heat cannot reach the control circuit. This prevents an overheating of the control circuit above the temperature of the cooling water.
An annular attachment of the excitation device around the pump chamber also achieves the fact that the waste heat of the excitation device can also be effectively emitted to the surroundings of the pump, i.e. to the motor chamber in the case of a motor vehicle cooling water pump. This excitation device can be suitably embodied as a claw-pole device.
The provision is also made that the impeller wheel is comprised of a magnetic material, at least in the vicinity of the range of a magnetic field that can be generated by the excitation device. As a result, the impeller itself assumes the function of a rotor which interacts directly with the excitation field, which permits a more lightweight and compact construction of the pump.
The control circuit is preferably disposed on an end wall of the pump chamber. This permits a favorable thermal shielding of the control circuit by the excitation device with a simultaneously compact design and it also permits a magnetic field sensor, which is possibly required for detecting the position of the impeller wheel and must be disposed close to the impeller wheel in order to be effective, to be combined into a single unit with the rest of the control circuit, preferably an integrated circuit.
The pump suitably includes a first housing part, for example made of a temperature resistant plastic, which constitutes a for example a cylindrical side wall and a first end wall of the pump, where an annular hollow space is formed between the side wall of the pump chamber and an outer wall of the first housing part and this annular hollow space contains the excitation device. This housing part, as will be explained in further detail below, is important for a simple assembly of the pump.
A second housing part suitably closes the annular hollow space and defines a chamber for the control circuit.
According to a preferred exemplary embodiment (FIG. 1), the control circuit is mounted in thermal contact with the end wall so that its temperature can be reliably limited by the temperature of the pumped fluid. In this instance, a plug for the electrical power of the control circuit is suitably connected to the end wall. Electrical conductors to and from the control circuit are incorporated into the end wall. This can be executed in such a way that the end wall or the first housing part to which it belongs is embodied as an MID (molded interconnection device), i.e. as an injection molded part with metallized zones, or that conductors in the form of stamped gratings are inserted into the end wall.
The embodiment of the control circuit as an integrated circuit with connections bonded to the electrical conductors permits the use of solder to be completely eliminated on and in the control circuit.
Other preferred exemplary embodiments (FIGS. 2 and 3) provide that the control circuit is mounted in thermal contact with the second housing part. In this instance, plugs and electrical conductors can be formed onto or embedded in the second housing part in a manner similar to that mentioned above in connection with the end wall.
The necessary electrical connections between some of the above-mentioned conductors and the excitation device are preferably produced in a form-fitting manner, particularly by means of resistance welding or ultrasonic welding or by means of hot staking.
The control circuit is preferably embedded in a heat conducting gel or resin, not least to protect it from being touched and contaminated.